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I gave myself a promise to stop spending time and money on my car and just keep driving it. Like most promises, this one did not last long...

I decided to investigate why the radio sound in my car was so lousy, even by 1998 standards.

The main reason: the foam on the door woofers has decomposed.

The second reason: all four "subwoofers" - as BMW calls them - were missing.

So the first step was obvious: I went and bought the best speakers I could afford, spending a hefty sum of 120 dollars. The midrange speakers and the tweeters seemed to be OK, so I decided to keep them.

That made the radio sound pretty good, even with the pathetic 4-inch "subwoofers" still missing. But now I wanted more...

I took a long look at the factory amplifier. Expensive, sophisticated, loaded with the bleeding edge DSP technology from 1990s. And just as lousy as any other factory car amplifier.

So I decided to replace it with an Alpine MRP-F320 I saved from my last car. It's an old and inexpensive amp, but it's well built and has plenty of power for my needs - 4 channels at 40 watts RMS each and a subwoofer channel at 120 watts RMS.

Problem is, the new amplifier did not fit on the original bracket in the trunk. It is wider and taller, and of course the mounting holes don't match. So I made some adapters...

Next step: the head unit. My plan is to reuse the original car wiring, without pulling new wires or cutting/splicing the existing ones. This car had its share of sloppy repairs, I don't want to hurt it any more.

So I bought a harness adapter on eBay and rewired it for my needs:

Then I pulled the radio out...

There is very little free space inside the single-DIN pocket. It was challenging to make all the wiring and the connectors fit behind the new radio. I had to pull the DSP, MID and IHKA to get my hands in there:

Well, that's all for now. Stay tuned, I will keep reporting my progress for the next few days.

Unfortunately, I have a big problem. Unshielded wires don't work too well. You can hear the noise from the I-Bus bleeding through. Not too loud, but you can hear it if you turn the music down to minimum volume.

At this point I have two options.

Option one: Run 2 channels of audio instead of 4 so I could use the existing twisted pairs. But then I would lose the fader function and the individual speaker delay adjustment.

Option two: Run a new shielded cable from the dashboard to the trunk. Sounds like a huge pain. Has anyone here done it? What does it take?

A problem with paying for audio installs is that a paid mechanic will not spend hours soldering wire harnesses and taking apart half of the car interior to route them properly. He will more likely add an amplifier to the speaker outputs of the original audio system, clip wires on with Scotchloks, tuck the cables under the carpet and move on to the next customer. I'm not a perfectionist, but I can't tolerate %^*** like this in my car:

Final view of the amplifier/crossover assembly. All 14 speakers are wired, all cables are neatly tied (except for that thin blue wire which I will take care of eventually). The factory wiring is intact in case the car ever becomes collectible and I want to put the original radio back.

I took the best microphone I had laying around and tried to do some (pseudo)scientific measurements.

Unfortunately, as soon as I played some 1kHz tone, I immediately heard something bad: nonlinear distortion coming from the front speakers. A quick look at the spectrum confirmed it: instead of a single 1kHz peak I saw a trail of harmonics.

A short investigation revealed the source of the problem: the 3-way crossovers I used for the front doors. You wouldn't think that a circuit of capacitors and inductors can be nonlinear, but apparently it can with a careful selection of lousy components.

The capacitors look and measure fine, but the big coils... This is the weirdest-looking ferrite I have ever seen:

I suspect that it's the ferrite core going into saturation and causing the nonlinearity. Can't think of anything else, but I'm open to ideas.